Braking controller of a three-phase permanent magnetic brushless DC motor for directly driving a screw pump

ABSTRACT

A braking controller of a three-phase permanent magnetic brushless DC motor for directly driving a screw pump includes a detection circuit for detecting power supply states of the three-phase permanent magnetic brushless DC motor and a braking circuit for controlling the braking startup according to the power supply states of the three-phase permanent magnetic brushless DC motor. When the motor is supplied with power, the braking circuit is cut off. When the motor is not supplied with power and the screw pump drives the motor to reverse, the braking circuit starts up.

TECHNICAL FIELD

The present invention pertains to a braking controller of motor directdrive oil-extracting screw pump; in particular, to a braking controllerof the reversal speed inhibition of three phase permanent magnetbrushless direct current motor for direct drive screw pump.

BACKGROUND OF THE INVENTION

Screw pump belongs to high efficiency oil-extracting apparatus, thereare two main reasons for the shutdown and reversal of motor of the screwpump:

1. When the rotator is made to rotate by the drive device of rod pump,elastic deformation will be produced in the long polished rod. Thedownhole rotator starts rotate after the most apex of polished rodrotates for tens of cycles, the elastic energy of these tens of cycleswill be released when shutdowns, thus the parts of the polished rodclose to ground will reversely rotate back with high speed if noinhibition is applied, the high speed reverse rotation will lead toreversal tripping accident of polished rod because the polished rod isformed by many nodes connected to each other (except continuous rod). Toensure the safety of polished rod, braking means must be employed.

2. When shut downs, the reflux of liquid will be produced by the actionof liquid pressure and pipeline pressure in the tubing and will drivethe rotator of screw pump to rotate reversely with high speed like ahydro-generator, such phenomena will happen in both ground drive rodpump and rodless pump submerged in the oil downhole. When liquid flowsreversely, the part of the transmission shaft connected to the rotatorwill always be broken by the drastic liquid reflux (especially forsubmerged rodless pump).

At present, there are two main braking means are employed by screw pump:the first one is stop reversal by ratcheting, this means is a type ofmechanical absolute reversal stop and does not allow the polished rodrotate reversely, this means has a simple structure while thereliability is poor, at the same time, it also has the problems such as:the initial torque is too great and will cause a starting impact whenrestarts, and the elastic transformation must be released in workoveroperation, mechanical damage or human injury accidents will be causedwhen operation is not suitable. The second is stop reversal by hydraulicpressure, which has a high reliability, however, the cost is high andthe structure is complex, thus the investment on apparatus is increased.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a braking controller of thereversal speed inhibition of motor for direct drive screw pump, toovercome the disadvantages of mechanical braking of screw pump.

The present invention relates to a braking controller of the three phasepermanent magnet brushless direct current motor for direct drive screwpump, which comprises: detecting circuit for detecting the state ofpower supply of the three phase permanent magnet brushless directcurrent motor; braking circuit for controlling the starting of brakeaccording to the state of power supply of the permanent magnetsynchronous motor, which is disconnected when power is supplied for themotor to work and can be started when no power is supplied to the motorand the motor rotates reversely driven by the screw pump.

The present invention installs a braking circuit on the three phasepermanent magnet brushless direct current motor for the direct drivescrew pump, through which successfully realizes the soft braking of thethree phase permanent magnet brushless direct current motor for thedirect drive screw pump, and the elastic force of the polished rod ofthe screw pump can be sufficiently slow be released, thus overcome thedisadvantage of mechanical braking.

The braking controller of the three phase permanent magnet brushlessdirect current motor for direct drive screw pump of the presentinvention, in which the detecting circuit comprises: a motor controller,current transformer L, normal-closed relay MJ, in which the detectingcircuit connects between the any two phases of the three phase currentinput terminal of motor controller, current transformer closes to thethree phase current output terminal of the motor controller, the currenttransformer connects to normal-closed relay in series, the brakingcircuit comprises: three large power energy consumption resistances RA,RB and RC connected in series on the three phase current output circuitof the motor controller, in which each energy consumption resistancesconnects to the contacts MJ-A, MJ-B or MJ-C of normal-closed relay inseries.

The braking controller of the three phase permanent magnet brushlessdirect current motor for direct drive screw pump of the presentinvention, in which the detecting circuit comprises: a motor controller,current transformer L, normal-closed relay MJ, rectifier diodes Q1 andQ2, rectifier triodes V and current limiting impedance element Z1, inwhich the detecting circuit connects between the any two phases of thethree phase current input terminal of motor controller, currenttransformer L closes to the three phase current output terminal of themotor controller, the current transformer L and normal-closed relay,rectifier diodes Q1 and Q2, rectifier triodes V and current limitingimpedance element Z1 connect in series, the braking circuit comprises:three large power energy consumption resistances connected in series onthe three phase current output circuit of the motor controller, in whicheach energy consumption resistance RA, RB and RC connect to one of thelarge power bidirectional triode thyristor MC-A, MC-B or MC-A in series,the state of turn-on of the large power bidirectional triode thyristoris controlled by the normal-closed relay.

When power is supplied for the motor to work, the screw pump is drivento forward rotate and induction current is generated by currenttransformer, two terminals of normal-closed relay are charged, thecontact of the normal-closed relay disconnects, that is the brakingcircuit does not start and the energy consumption resistance is notconnected. When the power supplied for the motor is stopped, noinduction current exists in the current transformer, two terminals ofnormal-closed relay are not charged, the contact of the normal-closedrelay MC-A, MC-B and MC-C connects, the braking circuit starts and theenergy consumption resistance RA, RB and RC connects; at this time, therotator of screw pump rotates reversely and drives the motor rotatereversely, the state of permanent magnet motor changes to the workingstate of generator, since the he energy consumption resistance has afixed resistance, the braking torque of the generator is higher when thespeed of reverse rotation is higher, thus inhibits the speed of reverserotation and realizes the soft braking of the motor.

Advantageous Effect:

The braking controller of the present invention has a simple structure,convenient operation and good braking property. The mechanical brakingapparatus of screw pump is omitted and the disadvantage of mechanicalbraking is overcome. When used on rod direct drive screw pump, saidbraking controller can release the elastic force of the polished rodsufficiently slow; when used on submerged rodless pump, said brakingcontroller can prevent the break of transmission shaft due to the refluxof liquid. After shutdown is stabilized, the initial torque of nextstarting is very small and easy to be started, reverse rotation willalso not happen in workover operation and accidents can be prevented.

The braking controller of the present invention can save energyconsumption. Since said braking is achieved by the electric braking ofthe power generated by the reverse rotation of generator, a higheracceleration of reverse rotation will lead to a higher electric braking,finally the elastic energy of polished rod and reflux energy of liquidis slowly released completely and back to the initial state, thusrealizes the soft braking. Therefore, no external energy is required forbraking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the circuit block diagram of the braking controller of motordirect drive oil-extracting screw pump according to the presentinvention.

FIG. 2 is the circuit principle diagram of the braking controller ofmotor direct drive oil-extracting screw pump according to the presentinvention.

FIG. 3 is the circuit principle diagram of the braking controller of themotor direct drive oil-extracting screw pump according to the preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1 (see FIG. 2)

The braking controller of the three phase permanent magnet brushlessdirect current motor for direct drive screw pump of the presentinvention, in which the detecting circuit comprises: a motor controller1, current transformer 2, normal-closed relay 3, in which the detectingcircuit connects between the any two phases of the three phase currentinput terminal of motor controller, current transformer closes to thethree phase current output terminal of the motor controller, the currenttransformer connects to normal-closed relay in series, the brakingcircuit comprises: three large power energy consumption resistances 4connected in series on the three phase current output circuit of themotor controller, in which each energy consumption resistances connectsto the contacts 5, 6 or 7 of normal-closed relay in series.

When power is supplied for the motor to work, the screw pump is drivento forward rotate and induction current is generated by currenttransformer, two terminals of normal-closed relay are charged, thecontact of the normal-closed relay MC-A, MC-B and MC-C disconnects. Whenthe power supplied for the motor is stopped, no induction current existsin the current transformer, two terminals of normal-closed relay are notcharged, the contact of the normal-closed relay MC-A, MC-B and MC-Cconnects, the energy consumption resistance RA, RB and RC connects, thebraking circuit starts at this time. Since the permanent magnet motorstop working, the rotator of screw pump rotates reversely and drives themotor rotate reversely. The state of permanent magnet motor changes tothe working state of generator at this time, since the he energyconsumption resistance has a fixed resistance, the dynamic torque of thegenerator is higher when the speed of reverse rotation is higher, thusinhibits the speed of reverse rotation of the motor.

Embodiment 2 (see FIG. 3)

The braking controller of the three phase permanent magnet brushlessdirect current motor for direct drive screw pump of the presentinvention, in which the detecting circuit further comprises: a motorcontroller 1, current transformer 2, normal-closed relay 3, rectifierdiodes 8, rectifier triodes 9 and current limiting impedance element 10,in which the detecting circuit connects between the any two phases ofthe three phase current input terminal of motor controller 1, currenttransformer 2 closes to the three phase current output terminal of themotor controller, the current transformer 2 and normal-closed relay 3,rectifier diodes 8, rectifier triodes 9 and current limiting impedanceelement 10 connect in series, the braking circuit comprises: three largepower energy consumption resistances are connected in series on thethree phase current output circuit of the motor controller, in whicheach energy consumption resistance 4 connects to one of the large powerbidirectional triode thyristor 11, 12 or 13 in series, in which thestate of the large power bidirectional triode thyristor 11, 12 or 13 iscontrolled by the normal-closed relay to be turn-on.

When power is supplied for the motor to work, the screw pump is drivento forward rotate and induction current is generated by currenttransformer, two terminals of normal-closed relay are charged, thecontact of the normal-closed relay MC-A, MC-B and MC-C disconnects, thelarge power bidirectional triode thyristor MC-A, MC-B and MC-Cdisconnects; when the power supplied for the motor is stopped, noinduction current exists in the current transformer, two terminals ofnormal-closed relay are not charged, the contact of the normal-closedrelay MC-A, MC-B and MC-C connects, the large power bidirectional triodethyristor MC-A, MC-B and MC-C connect, the energy consumption resistanceRA, RB and RC connects, the braking circuit starts at this time. Sincethe permanent magnet motor stop working, the rotator of screw pumprotates reversely and drives the motor rotate reversely. The state ofpermanent magnet motor changes to the working state of generator at thistime. Since the he energy consumption resistance has a fixed resistance,the dynamic torque of the generator is higher when the speed of reverserotation is higher, thus inhibits the speed of reverse rotation of themotor.

1. A braking controller of a three phase permanent magnet brushlessdirect current motor for direct drive screw pump comprises: detectingcircuit for detecting the state of power supply of the three phasepermanent magnet brushless direct current motor; braking circuit forcontrolling the starting of brake according to the state of power supplyof the permanent magnet synchronous motor, characterized in that thebraking circuit starts when no power is supplied to the motor and themotor rotates reversely driven by the screw pump.
 2. The brakingcontroller of the three phase permanent magnet brushless direct currentmotor for direct drive screw pump according to claim 1, characterized inthat the detecting circuit comprises: motor controller, currenttransformer (L), normal-closed relay (MJ), in which the detectingcircuit connects between the any two phases of the three phase currentinput terminal of motor controller, current transformer closes to thethree phase current output terminal of the motor controller, the currenttransformer and normal-closed relay connect in series; the brakingcircuit comprises: three large power energy consumption resistances (RA,RB and RC) connected in parallel on the three phase current outputcircuit of the motor controller, in which each energy consumptionresistance connects with the contacts MJ-A, MJ-B or MJ-C ofnormal-closed relay in series.
 3. The braking controller of the threephase permanent magnet brushless direct current motor for direct drivescrew pump according to claim 1, characterized in that the detectingcircuit comprises: motor controller, current transformer (L),normal-closed relay (MJ), rectifier diodes (Q1 and Q2), rectifiertriodes (V) and current limiting impedance element (Z1), in which thedetecting circuit connects between the any two phases of the three phasecurrent input terminal of the motor controller, current transformer (L)closes to the three phase current output terminal of the motorcontroller, the current transformer (L) and normal-closed relay (MJ),rectifier diodes (Q1 and Q2), rectifier triodes (V) and current limitingimpedance element (Z1) connect in series; the braking circuit comprises:three large power energy consumption resistances connected in parallelon the three phase current output circuit of the motor controller, inwhich each energy consumption resistance (RA, RB or RC) connect to oneof the large power bidirectional triode thyristor (MC-A, MC-B or MC-A)in series, the state of turn-on of the large power bidirectional triodethyristor is controlled by the normal-closed relay.